The present disclosure generally relates to an air leak determination system and method for an internal combustion engine, and more particularly to an air leak determination system and method that includes determining whether to prohibit detection of an air leak at the intake manifold of the engine under certain operating conditions.
By way of background, some vehicles cut fuel to the vehicle's engine when a significant air leak is detected in the engine's intake manifold to stall the engine and prevent the vehicle from running. These vehicles typically include an electronic control unit (ECU) connected to the engine that is capable of commanding a fuel cut to effect stalling of the engine whenever a significantly large air leak is detected at the engine's intake manifold. One conventional method for detecting an air leak in or at the intake manifold, sometimes employed as a secondary or auxiliary air leak detection method, is for the ECU to compare intake manifold pressure to atmospheric pressure, such as when the vehicle's throttle closes completely. Should the intake manifold pressure approach atmospheric pressure or some predetermined threshold, the ECU can presume that a significantly large air leak is occurring in or at the intake manifold and then effect the aforementioned fuel cut operation.
Some vehicles also cut fuel to the vehicle's engine when a misfire condition within the engine is detected. Typically, a misfire condition is detected on a cylinder-by-cylinder basis and the supply of fuel is cut from the bank of cylinders (e.g., left bank and right bank) in which the offending cylinder resides. One purpose for cutting fuel to a misfiring cylinder is to prevent the catalytic converter from being destroyed via overheating. When fuel is cut to a bank of cylinders, such as in response to a cylinder misfire, comparing intake manifold pressure to atmospheric pressure or to a predetermined threshold for determining that an air leak is occurring in the intake manifold can yield an inaccurate determination of an air leak occurrence, particularly when the vehicle is operated at relatively high altitudes where low pressures (e.g., pressures below about 550 mmHg) are encountered. In other words, when one side bank of cylinders has its supply fuel cut, such as in response to a detection of a cylinder misfire in that side bank, intake manifold pressure may approach atmospheric pressure or some predetermined pressure threshold under some operating conditions without an air leak occurring in the intake manifold.
Another situation in which detection of an intake manifold air leak by comparing intake manifold pressure to atmospheric pressure or a predetermined threshold may fail is when a vehicle equipped with a variable cylinder management (VCM) system has a failure detection system that detects failure of the VCM system, such as a failed or stuck cylinder stop solenoid valve. One or more cylinder stop solenoid valves are used in a VCM system for inactivating a predetermined number of cylinders under certain operating conditions, such as during deceleration of the vehicle. In particular, the one or more cylinder stop solenoid valves can be used to selectively permit oil pressure to reach a cylinder deactivating device that hydraulically prevents operation of the intake and exhaust valves corresponding to the cylinders being deactivated. When a cylinder stop solenoid valve fails, it often fails in the open position allowing oil pressure to continue to reach the cylinder deactivating device and thereby maintaining the predetermined one or more cylinders to be deactivated in a deactivated state. Similar to when one side bank of fuel is cut, a failed cylinder stop solenoid valve causing a predetermined number of cylinders to remain deactivated can also cause intake manifold pressure to approach atmospheric pressure or a predetermined threshold even when no significant air leak is occurring at the intake manifold, particularly when the vehicle is operated at relatively high altitudes.